A position sensor can detect the presence and location of a touch by a finger or by an object, such as a stylus, within an area of an external interface of the position sensor. In a touch sensitive display application, the position sensor enables direct interaction with information displayed on the screen, rather than indirectly via a mouse or touchpad. Position sensors can be attached to or provided as part of devices with a display, including but not limited to computers, personal digital assistants (PDAs), satellite navigation devices, mobile telephones, portable media players, portable game consoles, public information kiosks, and point of sale systems. Position sensors have also been used as control panels on various appliances.
There are a number of different types of position sensors/touch screens, such as resistive touch screens, surface acoustic wave touch screens, capacitive touch screens etc. A capacitive touch screen, for example, may include an insulator, coated with a transparent conductor in a particular pattern. When an object, such as a finger or a stylus, touches the surface of the screen there is a change in capacitance. This change in capacitance is measured by a controller and processed to determine the position of the touch.
In a mutual capacitance configuration, for example, an array of conductive drive electrodes or lines and conductive sense electrodes or lines arranged in two separate spaced apart layers can be used to form a touch screen having capacitive nodes. A node is formed at each intersection of drive and sense electrodes. The electrodes cross at the intersections but are separated by an insulator so as to not make electrical contact. In this way, the sense electrodes are capacitively coupled with the drive electrodes at the intersection nodes. A pulsed or alternating voltage applied on a drive electrode will therefore induce a charge on the sense electrodes that intersect with the drive electrode. The amount of induced charge is susceptible to external influence, such as from the proximity of a nearby finger. When an object touches the surface of the screen, the capacitance change at every individual node on the grid can be measured to determine the location or position of the touch.